Coasters are typically small pieces of wood, plastic, stone, paper, or other material people put on a surface (i.e., a wood table). Coasters protect the surface from heat of a beverage (e.g., hot tea or coffee) or liquid formed by the beverage (e.g., formed by condensation on the outside wall of a cold drink). Coasters may also be decorative in nature. They may be printed or embedded with promotional logos.
Sometimes, it is necessary or desirable that the temperature of a cold drink be maintained or a warm drink be cooled down and then kept cool for an extended period of time, e.g., for at least half an hour. There is a need for a coaster that can keep a drink cold for an extended period of time.